Mark E. Kraemer

Effects of ozone on soybean resistance to the mexican bean beetle (Epilachna varivestis mulsant)

Abstract Two soybean [Glycine max (L.) Merr.] cultivars, Forrest and Essex, were exposed to incremental levels of O3 in open-top field chambers during the 1986 growing season. Treatments consisted of chambers receiving carbon-filtered air or non-filtered air to which either 0.00, 0.03 or 0.06 ppm (μl/l)O3 was added continuously for 7 hr/day. After 3 weeks of exposure, the feeding preference of Mexican bean beetle (MBB) adults (Epilachna varivestis Mulsant) was determined by placing plants in a carbon-filtered chamber enclosed by an aluminum screen. Defoliation was visually determined after the MBB had fed for 6–8 days. Leaves from the remainder of the plants were brought to the laboratory and fed to MBB larvae. The larvae were reared in plastic boxes until pupation, and developmental time, pupal weight and mortality were determined. Visible O3 injury increased significantly with increasing O3 concentration and Forrest was significantly more sensitive than Essex. No cultivar differences were found in MBB adult feeding preference, but defoliation increased significantly with increasing O3 concentration. Results, although not as definitive as in the feeding preference study, indicated that MBB larvae tended to weigh more and develop faster on ozonated foliage. Implications of this pollutant × pest interaction are discussed relative to its potential impact on crop production.

Flower Phenology and Pollen Choice of Osmia lignaria (Hymenoptera: Megachilidae) in Central Virginia

Abstract Interest in native bees as alternative pollinators of agricultural crops has greatly increased in recent years. These bees do not produce honey but are often excellent pollinators, not aggressive, and not subject to a multitude of pest and regulatory problems. Herein we report the results of a 2-yr study of the eastern subspecies of Osmia lignaria Say, a univoltine, early-spring, mason bee. Our objective was to determine pollen choice of a wild population of O. lignaria lignaria Say throughout the period of nest construction and relate this to the phenology of local floral resources. Artificial nesting sites were provided and pollen provisions were sampled from nest cells constructed over a 7-wk period. Pollen was identified and quantified with scanning electron microscopy. Approximately 20 types of pollen were found in bee nest provisions, selected from 80 flowering species. Pollen choice changed over time in accord with flower phenology and pollen availability. Eastern redbud (Cercis canadensis L.) pollen was the most abundant (28%) in nest provisions, and bloom was coincident with initial spring nest construction. Nest provisions had 11% oak (Quercus sp.), 10% boxelder (Acer negundo L.), 10% mustard (Brassicaceae), 8% willow (Salix sp.), 7% ash (Fraxinus sp.), 6% blackberry (Rubus sp.), 4% black gum (Nyssa sylvatica Marsh), and 4% poison ivy (Toxicodendron radicans L. Kuntze) pollen. Maximum nest cell construction coincided with apple bloom and continued for several additional weeks. Floral resources were identified that could be used by eastern orchardists to attract and enhance local populations of O. lignaria lignaria.

Leaf Peltate Glandular Trichomes of Vernonia galamensis ssp. galamensis var. ethiopica Gilbert: Development, Ultrastructure, and Chemical Composition

Plants from the genus Vernonia produce a variety of flavonoids and bitter sesquiterpene lactones important for agriculture and human health. Leaf glandular trichomes of Vernonia galamensis ssp. galamensis var. ethiopica Gilbert (VGAE) were investigated for ultrastructural development and content composition because sesquiterpene lactones that impart a bitter taste to the leaves have been associated with the presence of these glands. Trichome ultrastructure was examined using LM, SEM, and TEM. Glands were removed from the leaf surface, and the chemical composition of gland contents was determined using HPLC and high‐resolution mass spectrometry. Immature and mature 10‐celled peltate biseriate glandular trichomes were present only at the abaxial side of the leaf. A large subcuticular space (head) developed from the most distal cell pair of the mature trichome and gradually filled with an osmiophillic substance. Mass spectrometry analysis revealed that the peltate trichome is a major source of prevernocistifolide‐8‐O‐isobutyrate. This glaucolide‐type sesquiterpene lactone was previously identified as a major constituent of the aerial parts of VGAE.

Insect Resistance in Vegetable and Tofu Soybeans1

Ten tofu and 14 green-vegetable soybean, Glycine max (L.) Merrill, genotypes were evaluated over 3 yrs for resistance to defoliation by the corn earworm, Helicoverpa zea (Boddie), and seed damage by a hemipteran complex. Petri-dish assays were used to determine foliar antibiosis to corn earworm. Larvae were weighed after feeding for 10 d on excised soybean leaves. Hemipteran damage was determined at harvest by individually rating 300 randomly sampled seeds from each subplot for severity of damage and calculating a weighted damage index. The specialty soybeans most resistant to corn earworm defoliation were Tousan 122, Guanyun da hei dun, and Enrei; whereas, those with the least seed damage were Barc-8 and Houjaku. There was no significant (F = 1.193; df = 1,300; P < 0.276) correlation of larval weight with seed damage index. It is likely that different mechanisms are responsible for seed and foliage resistance. There was a small but significant correlation (F = 40; df = 1,300); P < 0.001, R2 = 0.12) of se...

Evaluation of Vegetable Soybean Genotypes for Resistance to Corn Earworm (Lepidoptera: Noctuidae)

Petri dish bioassays were used to evaluate terminal foliage from 47 field-grown genotypes of vegetable-type soybean, Glycine max (L.) Merrill, from maturity groups III through VIII, for resistance ...

Emergence Phenology of Osmia lignaria subsp. lignaria (Hymenoptera: Megachilidae), Its Parasitoid Chrysura kyrae (Hymenoptera: Chrysididae), and Bloom of Cercis canadensis

ABSTRACT Emergence patterns of a natural population of Osmia lignaria subsp. lignaria Say were monitored during a 5-yr period (2003–2007) in relation to air temperature, bloom of eastern redbud (Cercis canadensis L.), and emergence of the parasitoid Chysura kyrae Krombein. Bee cocoons were placed in gelatin capsules and overwintered within shelters in their natural habitat. Mean emergence of female O. l. lignaria was observed at ≈2 d after redbud bloom began; mean male emergence was ≈ 1 wk earlier than for females and was nearly identical to that of C. kyrae. Horticultural models used to predict budburst for several tree species were evaluated with respect to redbud bloom and O. l. lignaria emergence. Each model indicated that both sexes of the bee and redbud had similar chill unit requirements. Differences in emergence and bloom dates were attributed to the different requirements for growing degree hours (GDHs) after chilling requirements were met. The close phenological relationship observed between eastern redbud and bee emergence suggests an important role for this common understory tree in the early nesting success of O. l. lignaria.

Nesting and Pollen Preference of Osmia lignaria lignaria (Hymenoptera: Megachilidae) in Virginia and North Carolina Orchards

ABSTRACT Cavity-nesting megachilid bees in the genus Osmia, found throughout the Palearctic and Nearctic regions, are good candidates for domestication. In North America, Osmia lignaria Say has been reported to be an excellent pollinator of tree fruit and is currently being developed for commercial use in orchards. This is largely because of research over several decades with the western subspecies of this bee, Osmia lignaria propinqua Cresson, in western orchards. The behavior of the eastern subspecies, O. lignaria lignaria Say, in eastern orchards has not previously been reported. This study evaluated the nesting activity and pollen preference of a population of the eastern subspecies in five orchards in the foothills and piedmont regions of North Carolina and Virginia over a 2-yr period. Apple was present in all orchards and all were bordered by hardwood forest. Shelters were placed both within orchards and the forest border. Emergence dates, nest construction, and orchard bloom were monitored weekly. Bee populations increased by 2–3 times annually at most orchards. Pollen species comprising nest provisions from 720 individual nest cells were identified and quantified using scanning electron microscopy. The greatest amount of pollen (46–82%) was that of a small understory tree, Eastern redbud (Cercis canadensis L.), at all orchard sites where these trees were present nearby. The quantity of orchard pollen was relatively low, <20% at full apple bloom, except for one orchard (53%) without nearby redbud. O. lignaria lignaria appears to prefer Eastern redbud pollen over orchard pollen.